Yes, Lemon juice does remove some stains but you might prefer White Vinegar as it removes stains also.

I would imagine that your cleaning regime is to fault.

Using a non-drying organic oil is likely to result in it going rancid. And vinegar, after all, is acetic acid.

I am reluctant to recommend a solution without doing some trials to see how it responds. It may just need a thorough cleaning, or the finish may be irreversibly damaged and require stripping and refinishing.

In the future, I'd limit the vinegar and olive oil to your salad dressing.

I think the important thing to remember is that it is much easier to prevent than remove stains. On successful removal of your stain immediately wax, oil or polish your coffee table as appropriate to prevent further damage from occurring.